As the accuracy of an exposure apparatus increases, a movable stage apparatus loaded with a six-axis fine movement stage as a wafer stage has been employed. A stage apparatus of this type is disclosed in, e.g., Japanese Patent Laid Open No. 2000-106344. A general stage apparatus will be described below with reference to FIGS. 15 to 18.
FIG. 15 is a view schematically showing a general movement stage apparatus. A yaw guide 301 is formed on a stage surface plate 300, and a Y slider 302 guided by the yaw guide 301 and the stage surface plate 300 is formed. Air pads (not shown) are provided between the Y slider 302 and stage surface plate 300, and between the Y slider 302 and yaw guide 301. Accordingly, the Y slider 302 can slide in the Y direction.
An X slider 303 is formed to surround the Y slider 302. The X slider 303 is formed of an X upper plate 303a, X side plates 303b, and an X lower plate 303c, and is guided by the side surfaces of the Y slider 302. Air pads 380 are provided between the side surfaces of the Y slider 302 and the X side plates 303b. FIG. 18 shows this arrangement. An air pad (not shown) is provided also between the X lower plate 303c of the X slider 303 and the stage surface plate 300. Accordingly, the X slider 303 can slide in the X direction with respect to the Y slider 302. The Y slider 302 is slidable in the Y direction, as described above, and the X slider 303 is slidable in the X direction with respect to the Y slider 302. Hence, the X slider 303 can slide in the X-Y direction.
A fine movement stage 360 constituted by a six-axis fine movement linear motor and a fine movement top plate 361 is formed on the X upper plate 303a of the X slider 303. As shown in FIG. 16, the six-axis fine movement linear motor is constituted by two X fine movement linear motors 362, two Y fine movement linear motors 363, and three Z fine movement linear motors 364. Each fine movement linear motor is a linear motor which is formed of a hollow, elliptical, flat coil, and magnets and yokes sandwiching the flat coil from the two sides, and which utilizes a so-called Lorentz force. This linear motor generates a thrust in a direction perpendicular to the straight portion of the elliptical coil within a plane including the flat surface of the flat, elliptical coil. The flat surface of the elliptical coil of each X fine movement linear motor 362 is parallel to the X-Z plane and its straight portion is parallel to the Z axis. The flat surface of the elliptical coil (Y coil 363d) of each Y fine movement linear motor 363 is parallel to the Y-Z plane and its straight portion is parallel to the Z axis. The flat surface of the elliptical coil (Z coil 364d) of each Z fine movement linear motor 364 is parallel to the Y-Z plane and its straight portion is parallel to the Y axis. Thus, the elliptical coils of the X, Y, and Z fine movement linear motors 362, 363, and 364 generate forces in the X, Y, and Z directions, respectively. Thus, the six-axis fine movement stage 360 can drive in six directions, i.e., in the X, Y , and Z axis directions and about the X, Y, and Z axes.
Arrangements other than that described above are also possible. For example, the number of either the X or Y fine linear motor may be one.
In each fine movement linear motor, the coil (363d, 364d) is fixed to the X slider X upper plate 303a through a coil frame (363e, 364e), and a magnet (363c, 364c) and a yoke (363b, 364b) are fixed to the fine movement top plate 361 through a yoke fixing member (363a, 364a).
Linear motors (an X linear motor 320 and Y linear motors 340) are also used to drive the X slider 303 and Y slider 302, respectively. The Y linear motors 340 are connected to the Y slider 302 through wing plates 304. Each linear motor 340 for driving the Y slider 302 is of a stationary coil, moving magnet type, as shown in FIG. 17, which is a two-phase sine wave drive type linear motor which realizes long stroke driving by selecting two coils in accordance with the magnet positions and appropriately controlling the magnitudes and directions of currents. The stationary coil is formed of a coil frame 342 fixed to the stage surface plate 300 through legs 341, and coils 343 fixed to the coil frame 342. The moving magnet is formed of a pair of four-pole magnets 344 sandwiching the coils 343 from two sides, yokes 346 formed on the rear surfaces of the four-pole magnets 344, and movable element side plates 345, which connect the yokes 346. Each X linear motor has a similar arrangement to this.
The positions of the Y slider, X slider, and fine movement top plate are measured by sensors (not shown). Desirably, the Y slider 302 and X slider 303 are measured by laser interferometers each having at least one axis, and the fine movement top plate 361 is measured by a laser interferometer having at least six axes.
In the above arrangement, the X slider 303 is driven by the linear motor shown in FIG. 18 to move through a long distance in both the X and Y directions, and the fine movement top plate 361 is controlled at high accuracy by the six-axis fine movement linear motor shown in FIG. 16. The six-axis fine movement linear motor for controlling the fine movement top plate 361 utilizes the Lorentz force. Thus, even when the positions of the X and Y sliders 303 and 302 and of the fine movement top plate 361 change, the six-axis fine movement linear motor is not influenced by this change at all, so that high accuracy position control can be performed.
An exposure apparatus stage loaded with the six-axis fine movement stage 360 utilizing the Lorentz force on the X-Y stage in the above manner is advantageous in that it can perform high accuracy position control over a long stroke. However, as the six-axis fine movement stage 360 is loaded, the mass of the portion ahead of the X slider 303, i.e., the total mass of the X slider 303 and fine movement stage 360 increases. The exposure apparatus stage must be accelerated at a high acceleration in order to increase the productivity. When the total mass of the X slider 303 and fine movement stage 360 increases, even when the acceleration stays the same, the force necessary for acceleration increases in proportion to the mass.
In the arrangement of the stage apparatus described above, the force necessary for accelerating the X slider 303 and fine movement stage 360 in the Y direction is originally generated by the Y linear motors 340 shown in FIG. 17. Part of the generated force is transmitted to the X slider 303 and fine movement stage 360 through the air pads shown in FIG. 18. More specifically, the two Y linear motors each having the arrangement as shown in FIG. 17 generate a force of (m1+m2+m3)×α where m1, is the mass of the Y slider system, m2 is the mass of the X slider system, m3 is the mass of the fine movement top plate system, and α is the acceleration. Of the generated force, a force of(m2+m3)×α is transmitted to the X slider 303 and fine movement stage 360 through the air pads 380 shown in FIG. 18.
What matters is the force transmission ability of the air pads 380. Force transmission with the air pads 380 is suppressed to about 1 kgf/cm2 when converted into a pressure. Hence, by adding the fine movement stage, if the force of (m2+m3)×α increases, the air pads 380 can no longer transmit this force. Still, it is very difficult to form a rolling type stage with the air pads 380, due to the issues of the service life and dust. A rolling type guide is difficult to apply to a stage that must operate continuously over a long period of time and must have a high cleanliness as in an exposure apparatus. Hence, to form a noncontact guide cannot be given way.
In addition, recently, to expose a finer pattern, a stage that can be used in a vacuum atmosphere is required. To form air pads in a vacuum atmosphere, a means for collecting air must be provided in the periphery of the air pads. As this peripheral portion does not contribute to thrust transmission, the thrust transmission ability converted into the pressure tends to decrease more and more.
In view of the above situation, it is demanded to provide a stage apparatus which has a noncontact guide that can quickly accelerate a movable body loaded with a fine movement stage and having a large conveying mass.